1. Field of the Invention
The present invention relates to a multicylinder internal combustion engine in which the fuel supply to some cylinders is cut off, in accordance with the engine load so as to achieve partial cylinder operation, more particularly, to a device which enables any of the intake valves and exhaust valves of the cylinders to be idled during partial cylinder operated.
2. Description of the Prior Art
Under a light engine load, it is possible to improve the engine thermal efficiency by maintaining either the intake or exhaust valve of some of the cylinders or, in some cases, both the intake and exhaust valves, in a fully closed state so as to eliminate the pumping work of the idle cylinders. Maintaining the valves of the idle cylinders in a fully closed state prevents air from flowing from the idle cylinders to the exhaust system, thus also prevents cooling of the catalyst device located in the exhaust system and prevents decreased exhaust gas cleaning efficiency of the catalyst device.
Various proposals have been made for techniques to idle intake and exhaust valves for such reduced cylinder operation, but these have all had defects.
The present inventor previously proposed in Japanese Utility Model Application No. 56-57839 an improved valve stopping device of an internal combustion engine. In the previous proposal, valve stopping mechanisms were mounted for each pair of intake and exhaust valves. The valve stopping mechanisms were connected to each other with crank arms and a link mechanism for synchronized rotation.
The valve stopping device proposed by the present inventor comprised, rocker arms rocking along with the rotation of cams; an intake valve and exhaust valve biased in the closed direction by valve springs; rotors rotatably attached to valve shafts of the valves and engaging and disengaging with the ends of the rocker arms; a rotor connecting means which connects the rotors with crank arms and a link mechanism for synchronized rotation of the rotors; and a rotating means for the rotors. The intake valve and exhaust valve operated when the ends of the rocker arms engage with the rotors. The valves shut down operation and entered a closed state when the rocker arms and rotors disengaged. In this previous device, each rotor was provided with a pair of small projections at diametrically opposed sides thereof. The working ends of the rocker arms were branched so as to form two claws. The space between the two claws was slightly larger than the diameter of the cylindrical part of the rotors. The distance between the two claws corresponded to the distance between the two small projections of the rotor. When the small projections aligned with the claws, the rotor rose and fell following the cam rotation so that the valve operated to open and shut (hereinafter, simply "operated"). When the rotor rotated 90.degree. from that position, the claws at the end of the rocker arm straddled the cylindrical part of the rotor. Consequently, even if the rocker arm rocked, the rotor did not move. Thus, the valve shut down operation and enterned a closed state.
In the above stopping control device, however, when the engine speed was high, there was sometimes not enough time for the rotor to rotate 90.degree. between the compression stroke and expansion stroke. At such times, the rotor rotated only little by little until the claws would come off from the upper face of the small projections. Thus, the intake valve and the exhaust valve would remain in the operation shutdown state.
Likewise, when trying conversely to operate the intake valve and exhaust valve from the operation shutdown state during high engine speed, the claws would engage the small projections first, so the rotor would sometimes only rotate a little before it rotated to the predetermined position. At this time, the play in the link mechanism and/or the manufacturing tolerances of the rotor and the claws would sometimes cause either the intake valve or the exhaust valve to first become closed or to first begin operating.
If either the intake valve or exhaust valve changed in operation state before the other, when operating intake and exhaust valves were shifted to the operation shutdown state, the exhaust valve sometimes stopped or become closed first. Conversely, when the intake and exhaust valves in the operation shutdown state were shifted to the operation state, the intake valve sometimes began to operate first. In such cases, the air-fuel mixture, intake air, or burnt gas in the cylinders was blown back into the intake pipe, thereby impeding the driveability of the engine.